This invention relates to a method for distinguishing between field crops, particularly potatoes on one hand and stones or clods of soil on the other hand, whereby each of these pieces to be distinguished is allowed to drop onto a sensor and whereby distinguishing criteria of the impact of said pieces onto said sensor are detected. One prior method of this kind is based exclusively onto detection of distinguishing criteria of the mechanical impact (DE-OS No. 25 06 212). However, it was found that in this manner potatoes and clods of soil may only be distinguished from each other under particularly favorable circumstances regarding humidity and kind of the soil. Such a method is practically of no use and it has never been used on a larger scale in practice.